The present invention relates generally to communications networks and, more particularly, to methods and systems for establishing high-capacity connections in such networks.
In a communications network, traffic generally travels from a source to a destination though one or more intermediate nodes, also known as cross-connection hubs, which may be spaced hundreds of kilometers apart. Different geographical regions of a large network are usually owned and run by entities known as network operators, network administrators or telcos and several such network operators may join forces to establish a communications network which spans an entire country or continent.
Usually, the network operators serve to provide capacity which is then loaned to smaller entities known as service providers. Each such service provider may be desirous of establishing a relatively permanent, high-capacity connection between two points in the large network. Each such high-capacity connection may be intended to provide communications services for multiple end users, also known as subscribers. Thus, the high-capacity connection associated with a service provider may be referred to as a composite connection.
Each composite connection generally has a capacity that is still considerably less than the switching capacity of a single network node. Thus, several composite connections associated with different service providers and having their own respective sources and destinations may nevertheless be processed by the same switching node if it so happens that these composite connections share the same portion of the route which passes through the switching node in question. Therefore, it is often the case that individual switching nodes end up processing traffic streams belonging to multiple composite connections that are associated with different service providers.
In today""s networks, traffic commonly consists of digital frame-based signals which abide by a synchronous standard such as SONET (Synchronous Optical Network), which is described in Bellcore document GR-253-CORE, Issue 2, December 1995, Revision 2, January 1999, hereby incorporated by reference herein in its entirety. The elementary unit defined by the SONET standard is a synchronous transport signal having a line rate of 51.84 Mbps, commonly referred to as an STS level 1 (or STS-1) signal.
As is known in the art, each frame of an STS-1 signal has a relatively small number of bytes in a portion known as the xe2x80x9ctransport overheadxe2x80x9d and a significantly larger number of bytes in a portion known as the xe2x80x9csynchronous payload envelopexe2x80x9d (SPE). The transport overhead contains the so-called section overhead and line overhead, and it performs the functions needed to transmit, monitor and manage the SPE over a fiber system. It also contains an STS-1 payload pointer, which indicates the start of the SPE. For its part, the SPE consists of a path overhead and a payload. The path overhead supports the monitoring and management of the payload, while the payload carries the voice or data signals being transported.
In many cases, it is desirable to transmit signals at a rate higher than the relatively low basic SONET line rate of 51.84 Mbps. The SONET standard provides for at least two ways of transmitting higher-bandwidth signals at line rates that are a multiple of (e.g., N times) the basic SONET line rate of 51.84 Mbps. Both techniques involve mapping a high-rate data stream into the SPE of a high-rate SONET signal. Specifically, both techniques require initially chopping up the high-rate data stream into N SPE segments per frame.
Using a first technique, the SPE segments are then multiplexed on a byte-by-byte basis and transported by an STS-N signal. The individual SPE segments travel independently across the network and may reach their destination with slight relative delays. Hence, it is beneficial to employ this first technique when it is desired to transmit N independent STS-1 signals in parallel.
Using a second technique, the SPE segments are not multiplexed but rather are transmitted in strict order by an STS-Nc signal (known as a xe2x80x9cconcatenatedxe2x80x9d signal). The fact that the signal is concatenated is indicated by a special arrangement of bytes in the transport overhead of the STS-Nc signal which identify one of the portions of the SPE as being the last such portion in the frame. The STS-Nc signal carries the individual SPE segments, in order, until they reach their destination. Hence, it is beneficial to employ this second technique when it is desired to transmit a high-rate data stream which cannot be broken down into smaller components.
The hardware needed to process an STS-N signal is different from the hardware required to process an STS-Nc signal. For example, it is noted that in order to process an STS-N signal at a switching node, it is feasible to de-multiplex the STS-N signal into its N STS-1 components and to process each component separately. This is an advantage in situations where N is high and where a single ASIC (application specific integrated circuit) is incapable of processing the entire STS-N signal. In such a case, an appropriate number of additional ASICs can be provided to help process the N de-multiplexed STS-1 signals in parallel.
In contrast, an STS-Nc signal may not be broken up (e.g., through de-multiplexing) because the sequence of bytes in the SPE is important. In order not to break up the signal at each step of the way along its route, the same application-specific integrated circuit (ASIC) must usually be employed to process the entire STS-Nc signal.
Since the two types of higher-capacity signals have their own specific advantages and useful applications, it is usually the case that a composite connection to be established by a service provider will consist of both STS-N signals (for different values of N) and STS-Mc signals (for different values of M). In order to allow a particular combination of STS-N signals and STS-Mc signals to be transmitted, it is necessary for the service provider to verify with each network operator that suitable hardware resources are available along each segment of the route.
There are two main limitations which can affect the establishment of a composite connection for accommodating multiple lower bandwidth signals (including some STS-N signals and some STS-Mc signals). The first is strictly a capacity limitation, i.e., the hardware at each intervening node must have sufficient available resources to process the totality of signals in the composite connection. This can easily be verified by comparing the total available capacity of a node to the required capacity of the composite connection. The total available capacity will, of course, be affected by existing traffic (e.g., other composite connections) currently being handled by the node.
The second limitation is more subtle and is one which is imposed by the specific hardware configuration of each node. For instance, the available hardware must be distributed in such a way that it is capable of processing the concatenated signals forming part of the composite high-capacity connection. Some distributions of hardware will permit the processing of signals in one category (e.g., STS-N) while not allowing the processing of signals in another category (e.g., STS-Nc). Moreover, the manner in which the available hardware resources are distributed depends largely on the way in which the presently occupied resources were allocated for processing the signals belonging to the other composite connections currently passing through the node in question.
To consider a simple example, if a node is equipped with 4 ASICs, each of which has just enough residual capacity to process three STS-1 signals, then processing of an STS-12c signal cannot take place at the node in question, even though the total available capacity is sufficient to process an STS-12c signal. This is due to the fact that the entire STS-12c signal must be processed by a single ASIC, none of which is available in this case. Thus, it would not be possible to establish a connection for carrying an STS-12c signal.
Because of this second limitation, a connection request for an STS-Mc signal across a network must be handled differently from a connection request for an STS-M signal or M STS-1 signals or M/3 STS-3 signals, for example. Also, a connection request for an individual signal connection must also be treated separately from a request involving a combination of concatenated and non-concatenated signals. Simply put, in order to establish a connection made up of a given combination of signals, knowledge of the specific hardware at each stage of the connection and knowledge of the actual set of signals to be transmitted is required.
Clearly, current methods of establishing connections are inefficient in their usage of hardware resources and thus it would be of benefit to provide an improved and more efficient way of establishing connections between end points in a network.
The present invention is directed to a method for efficiently establishing connections along a route in a communications network. The concept of a content-flexible (or xe2x80x9copenxe2x80x9d) connection along the route is introduced. The establishment of an open connection corresponds to a reservation of appropriate hardware resources along the route. The manner in which the resources are allocated takes into consideration a maximum allowable capacity for the combination of signals to be carried by the open connection as well as a set of concatenation constraints which need to be satisfied by the combination of signals.
The resources are allocated in such a way as to allow the transport of any signal combination which satisfies the concatenation constraints and which has an aggregate capacity less than or equal to the maximum allowable capacity associated with the open connection. As a result, the signal make-up of the open connection can be changed as desired, without having to re-allocate the resources each time. Thus, the efficiency with which connections are established is improved by virtue of allowing a combination of signals transported as part of a pre-established connection to be changed at the end points of the route without having to reconfigure the hardware between the end points.
In addition, the invention offers advantages for the service provider and network operator, because these entities need not be concerned with resource allocation in response to unpredictable changes in the end user""s desired traffic mix.
It is also within the scope of the invention to provide for the establishment of one or more content-flexible connections at a higher network layer within a single, lower-layer content-flexible connection or within a cascaded set of lower-layer content-flexible connections. From a network management perspective, this allows diverse service providers to establish inter-city connections through multiple service areas in an initial phase and then to change the traffic mix within each such inter-city connection to suit end user needs, with the knowledge that a new traffic mix can be supported if it meets the initially specified concatenation constraints.
According to one embodiment of the present invention, there is provided a method of establishing a content-flexible connection along a route in a network, where the method includes the steps of determining a capacity associated with the connection; determining a set of concatenation constraints associated with the connection; and allocating selected resources along the route to allow the delivery of any combination of signals satisfying the determined set of concatenation constraints and having a total capacity not exceeding the determined capacity.
In some embodiments, the concatenation constraints are satisfied by a particular combination of signals if the particular combination of signals only includes signals selected from a pre-determined group of signals. In other embodiments, the concatenation constraints are satisfied by a combination of signals if that combination only includes signals selected from a first pre-determined group of signals or sub-combinations of signals which satisfy a second set of concatenation constraints, where the second set of concatenation constraints is satisfied by a sub-combination of signals if that sub-combination only includes signals selected from a second pre-determined group of signals.
In either case, the signals which make up the transported combination of signals can include concatenated signals and/or non-concatenated signals.
According to a further embodiment, the step of allocating selected resources may include, for each node along the route, identifying an external connection pattern which is consistent with the route; identifying a distribution of node-level resources which allows the hardware requirements associated with the node to be met; and allocating the identified distribution of node-level resources.
Before the step of allocating selected resources, there may be provided the step of determining, from the determined capacity and the determined set of concatenation constraints, a set of hardware requirements associated with each node along the route.
Other embodiments of the invention provide methods, controllers and computer usable media with computer-readable program code for processing a request for an open connection received at a central control unit, at a controller in a node or at a controller in a sub-node-level component.
According to another embodiment of the invention, there is provided a method of establishing at least one higher layer connection within a lower layer connection in a network. The method includes determining a first capacity associated with the lower layer connection; determining a first set of concatenation constraints associated with the lower layer connection; establishing the lower layer connection by allocating selected resources along the route to allow the delivery of any combination of signals satisfying the first set of concatenation constraints and having a total capacity not exceeding the first capacity. Finally, in this embodiment, the method includes for each of the at least one higher layer connection, using a respective subset of the allocated resources to carry a respective combination of signals satisfying a respective set of second concatenation constraints which is a subset of the first set of concatenation constraints.